We wish to continue multifaceted investigations of cerebral microcirculation. These studies include observations of microcirculation in experimental models of diseases characterized by altered blood viscosity; observations of the effects of seizures on microcirculation and microvascular control mechanisms; examination of some chemical agents that may effect microvascular diameters; studies of neurogenic influences on cerebral microcirclation. Techniques include measurements of red cell velocity and plasma transit time, utilizing high and low speed microcinematography; measurements of vascular diameters employing direct microscopic observation as well as closed circuit television monitoring; histochemical fluorescence measurements of norepinephrine content in perivascular nerves; and monitoring of changes in DPNH levels and oxygen availability in the brain during periods of microcirculatory stress.